So I'm learning about Pan-Asianism in my East Asian History course rn and in writing, it doesn't seem like it was a bad idea. I understand that the Japanese used it as a driving force to back up their attempts at imperializing Asia but are there any other reasons it failed?
I'm no expert on the subject, but I can reference a prior thread from u/netro (https://www.reddit.com/r/AskHistorians/comments/1zqg62/what_was_japans_plan_for_all_the_territories_it/) and u/pizzapicante27 (https://www.reddit.com/r/AskHistorians/comments/h7se8w/did_the_japanese_asian_coprosperity_sphere_ever/) that offer some good detail on the incoherence of the interplay between sincere/insincere Japanese overtures to pan-Asianism.
Besides this, I can also offer my two cents regarding the region as a whole. This varies on your definition of failure (and pan-Asianism for that matter), but Asia is obviously a big region. Political movements in different regions, say comparing China and India in the first half of the 20th century, are radically different in terms of ideological goals and aspirations. This is a major stumbling block to pan-Asianism, which is also hobbled by the more global context of the Cold War after the end of the World War 2 and the acceleration of decolonization. Continuing the China/India dichotomy, Nehru's and Mao's visions for how decolonized places should engage in the Cold War radically differ as well.